This section provides background information related to the present disclosure which is not necessarily prior art.
As is well known, water pumps are typically used in motor vehicles as part of a thermal management system for pumping a liquid coolant to facilitate heat transfer between the coolant and the internal combustion engine during vehicle warm-up and operation. Most commonly, a centrifugal water pump having a rotary pump member, such as an impeller, is configured to draw the coolant into an axial inlet and discharge the coolant through a radial discharge outlet. In many vehicular arrangements, the impeller is fixed to an impeller shaft that is rotatably driven (via an accessory drive system) by the crankshaft of the engine. Thus, the impeller speed is directly proportional to the engine speed. To provide a variable flow feature to such shaft-driven water pumps, it is known to permit limited axial displacement of the impeller within the pump chamber. For example, U.S. Pat. No. 7,789,049 discloses a water pump having an axially-moveable impeller that is spline mounted to the engine-driven shaft, and an electromagnetic actuator operable to control axial movement of the impeller between extended and retracted positions along the shaft so as to variably regulate the fluid flow characteristic between the fluid inlet and the discharge outlet. Similarly, U.S. Pat. No. 5,800,120 discloses a water pump having a shaft-driven impeller equipped with axially-moveable blades, the position of which is controlled via a hydraulic actuator.
It is also well known to install an auxiliary water pump, such as an electric water pump, in the engine coolant system to provide augmented control over the fluid flow. Generally, electric water pumps include an electric motor having a stationary stator and a rotor that is drivingly coupled to the impeller. Examples of electric water pumps are disclosed in commonly-owned U.S. Publication No. US2013/0259720 titled “Electric Water Pump With Stator Cooling” and U.S. Publication No. US2014/0017073 titled “Submerged Rotor Electric Water Pump with Structural Wetsleeve”, the entire disclosures of which are incorporated herein by reference. One drawback associated with many conventional electric water pumps is the need to provide a rotor encoder or another type of speed sensor within the electric motor to assist in accurate low speed (i.e. less than 600 RPM) pump control via a closed loop motor control system. Additionally, a need exists to provide variable flow at such low speeds that is not directly proportional to motor speed in an effort to meet customer expectations.
In view of the above, a need exists in the art to design and develop simplified and low-cost electric water pumps capable of providing variable flow characteristics and which can be easily substituted for otherwise conventional electric water pumps in motor vehicle applications.